Spark advance control mechanism



Jan. 18, 1955 E. A. VOGEL SPARK ADVANCE CONTROL MECHANISM Filed Oct. 6, 1950 i I /6 24 w -1 IN V EN TOR.

fiiwczrd' 0?. w 65 United States Patent O 2,699,657 SPARK ADVANCE CONTROL MECHANISM Edward A. Vogel, Beloit, Wis., assignor to Fairbanks, Morse & Co., Chicago, Ill., a corporation of Illinois Application October 6, 1950, Serial No. 188,818 1 Claim. (Cl. 64-25) This invention relates to improvements in a spark advance control mechanism. More particularly, it has to do with improved means for varying the range of spark advance of an ignition timing mechanism that is responsive to the speed of the engine.

In a well known type of ignition timing device, a centrifugal mechanism is employed to couple a driving shaft with a circuit breaker ca min such a manner that the cam will be driven with the driving shaft, while the angular relation between the cam and the shaft will be altered through a predetermined range in accordance with variations in the speed of rotation of the shaft. For best performance, different engine installations require diiferent ranges of spark advance from engine idling speed to operating speed. It is desirable, therefore, that some provision be made for varying the range of spark advance to accommodate different engines.

It is an important object of the present invention to provide convenient means to easily adjust the maximum range of ignition spark advance.

Another object of this invention is to provide an en closed ignition control mechanism including a casing having an access hole through which the mechanism may be conveniently adjusted.

According to the teachings of the present invention, a novel spark advance governor is provided which includes a pair of weights pivotally mounted on a rotat able base plate, and a control lever connected to a camshaft which is mounted for rotation about the axis of the base plate. Upright pins are secured to the free ends of the pivotable weights and arranged to engage in elongated, radially extending slots in the control lever to rotate the control lever and the camshaft relative to the base plate as the weights are pivoted due to centrifugal force occasioned by rotation of the base plate. Thus as the speed of the engine-driven base plate increases, the pins are moved radially outwardly in the slots of the control lever to advance the circuit breaker cam, the length of the slot determining the range of spark advance. In the arrangement indicated, an adjustable screw is threaded into an upstanding car at one end of the control arm, the inner-end of the screw extending out over the adjacent slot to define the elfective length of the slot and limit the outward movement of the pin therein. Moreover, the governor casing has an access port with a removable cover adjacent the head of the adjustable screw. When the cover is removed, a screwdriver can be inserted through the port for adjusting the screw.

A spring is connected between each and the base the cam.

Other and further features, objects, and advantages of the present invention will be apparent to one skilled in the art from the following detailed description taken in connection with the accompanying drawings.

On the drawings:

Figure 1 is a side elevational view, partly broken away and partly in section, of an ignition device incorporating a spark advance mechanism constructed in accordance with the teaching of the present invention.

Figure 2 is a vertical sectional view taken on line 2-2 of Figure 1.

Figure 3 is a vertical sectional view, similar to Figure 2, and showing a rotated positionof the control mechanism.

pivoting weight plate to yieldingly resist the advancing of Figure 4 is a fragmentary side elevational view taken on line 44 of Figure 3.

As shown on the drawings:

In Figure 1, the reference numeral 10 indicates an ignition device which has a three piece, separable casmg 11. One section of the casing is provided with a hub 13 in which a drive shaft 15 is journalled. A flange 16 provides means for mounting the device on an engine (not shown). The shaft 15 is driven from the engine through a clutch element 17 which is keyed to the shaft in any suitable manner and held thereon by a nut 18. Near its opposite end, the shaft 15 is connected in driving relation to a cam sleeve 20 through a centrifugal control mechanism 22. A two-lobe camming surface 21 of the cam sleeve 20 is movable against a breaker-arm 24 which is effective to interrupt the primary circuit of the ignition system in a manner well known in the art.

As best seen in Figure 4, the drive shaft 15 has a driving portion 15a of a smaller diameter than an engine driven portion 15b which is journalled in the hub 13. The driven portion 15b passes through and is rigidly secured, as by a press fit, in a central aperture in a circular support plate 26. Thus, rotation of the shaft 15 will cause rotation of the support plate 26.

The cam sleeve 20 is disposed in free, close-fitting en gagement over the driving portion 15a of the shaft 15 so that it may be rotated about the axis of the shaft. One end of the sleeve 20 abuts an annular shoulder 28, Figure 4, that is formed at the junction of the shaft portions 15a and 15b, while the other end of the sleeve is engaged by a spring clip 29 which is disposed in a suitable groove in the shaft 15.

The centrifugal control mechanism 22 is made up of a pair of laminated flyweights 31 each of which is pivotally mounted on a separate peg 32 which is secured to and projects outwardly from the support plate 26. The pegs 2 are diametrically opposed to each other and are located equidistantly from the axis of the shaft 15. The lamination 31a, of each weight 31, which is closest to the support plate 26 extends further away from the pivot point than the other laminations, thereby forming a support arm for a peg 33. The peg 33 is secured to each support arm by inserting a reduced diameter shank portion through an aperture in the arm and peening over the end of the shank against the opposite side of the arm, as at 35, Figure 4. Each of the pegs 33 pro-- ject through an elongated slot 37 in a control arm 38 that is secured to or integrally formed on the sleeve 20 near the end of the sleeve that abuts the shoulder 28. The control arm 38 is a generally rectangular, elongated member arranged symmetrically with respect to the sleeve 20, and wherein the slots 37 of the arm are of equal length and spaced equidistantly from the axis of the shaft 15.

It will now be evident that when the shaft 15 is rotated, the weights 31 pivot on the support plate 26 due to centrifugal force. The pegs 33, through their contact with the side walls of the slots 37, cause the control lever 38 to rotate and thus rotate the cam sleeve 20 relative to the shaft 15.

A tension coil spring 39 is connected between each upstanding peg 33 and an anchoring post 40, Figure 4, which is secured to the support plate 26 as by riveting. The springs 39 yieldingly resist centrifugal displacement of the weights and hence the rotation of the cam sleeve, and are effective to return the weights and the cam to initial position upon reduction in engine speed to idling or upon engine shut-down.

Ordinarily, the length of the slots 37 would determine the range of spark advance, since the radially outer end wall of the slots would arrest the movement of the pegs 33 and limit the pivoting movement of the weights 31. It is a particular feature of the present invention that the range of spark advance can be adjusted to obtain optimum operating conditions of the particular engine on which the magneto 10 is mounted.

This adjustment is obtained by means of a screw 41 that is threaded into a tapped aperture (not shown) in an upstanding ear 42 at one end of the control arm 38. As seen in Figure 3, the screw 41 overhangs the associated slot 37 and limits the outward movement of the peg 33. The screw 41 has a slotted outer end 43 and is locked in position by a locknut 44.

In Figure 2, the position of the governor mechanism when the engine is stopped or idling, is illustrated. In Figure 3 the maximum pivoted position of the speedresponsive weights is shown. It will be readily recognized that the range of spark advance can be increased by backing the screw 41 out of the ear 42, and that the range can be decreased by threading the screw further into the .ear.

Referring to Figure 1, it will be seen that the casing 11 is provided with a tapped opening 45 into which a plug 46 is threaded. The opening 45 is directly opposite the slotted end 43 of the screw 41 when the mechanism is in the position indicated in Figure 2. The plug 46 can be easily removed so that a screwdriver may be inserted through the opening 45 and into the slotted end 43 to regulate the range of spark advance. The locknut 44 may be manipulated by means of a suitable wrench also inserted through the opening 45.

From the foregoing description it will be seen that there is provided in this invention a novel, convenient device for varying the range of spark advance in a speed responsive ignition timer mechanism.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

In an ignition timer including a timer shaft and a cam shaft rotatably sleeved thereon, centrifugal timer control means connecting said cam shaft in driven relation to said timer shaft, said means comprising a support member fixed on said timer shaft; a laminated flyweight pivotally mounted at one end on said support member; one la t on e eme t he e t pro d g a e tens on beyond the opposite free end of the flyweight; a peg fixed to and outstanding on said extension; a flyweight loading spring between said peg and said support member; an arm member fixed to and extending radially of said cam shaft; said arm member having a radial elongated slot therein receiving said peg t-herethrough; a projection on the free end of said arm member; and a stop element carried by said projection and adjustably positionable longitudinally of said slot, provided for abutment by said peg to determine the limit of centrifugal displacement of the flyweight.

References Cited in the file of this patent UNITED STATES PATENTS 1,872,252 Darnell Aug. 16, 1932 2,008,647 Schneider July 16, 1935 2,219,480 Hartzell et al 'Oct. 29, 1940 FOREIGN PATENTS 425,240 Germany 1926 

